The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Combustion of an air/fuel mixture within cylinders of an engine yields exhaust gas, which is expelled from the cylinders into an exhaust system before being released into the atmosphere. The exhaust system includes a catalytic converter that reduces emissions that are present in the exhaust gas. The catalytic converter reduces emissions most effectively when the temperature of a catalyst within the catalytic converter is greater than or equal to an activation temperature.
When an engine is started after the engine is shutdown for an extended period, referred to as a cold start, the catalyst temperature may be less than the activation temperature. Thus, the ability of the catalytic converter to reduce emissions may be diminished. In addition, when the engine is started, the air/fuel ratio of the engine may be adjusted to a rich value to ensure that the engine starts. Thus, the exhaust gas may contain elevated levels of emissions such as hydrocarbons relative to normal operation. The diminished ability of the catalytic converter to reduce emission and the elevated levels of emissions due to rich operation may cause a greater amount of emissions to be released into the atmosphere during a cold start relative to normal operation.